The specific aims of this study are to: 1) evaluate the peak and steady state nicotine levels obtained from the 14 and 21 mg nicotine patch compared to ad lib smoking in pregnant women who smoke more than 15 cigarettes per day, and 2) determine the effects of a single dose of nicotine patch on the fetal parameters of heart rate, uterine, umbilical and cerebral blood flow. The study was then repeated in the same women in the non-pregnant state. It is hoped that this will allow the investigator to determine if the lower than expected nicotine concentrations found in smoking pregnant subjects were due to physiologic changes during pregnancy, or due to individualized smoking patterns among study participants. The study has been completed and the data are being analyzed.